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Creating Bytes from JSONValue with a Pointer #2

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Creating Bytes from JSONValue with a Pointer #2

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114 changes: 114 additions & 0 deletions Sources/PureSwiftJSONParsing/JSONValue.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -131,3 +131,117 @@ public func == (lhs: JSONValue, rhs: JSONValue) -> Bool {
return false
}
}

@available(*, deprecated, message: "Don't use this, this is slow")
class WritableBuffer {
private var ptr: UnsafeMutableRawBufferPointer

@usableFromInline typealias _Index = UInt32
@usableFromInline typealias _Capacity = UInt32

@usableFromInline var _index : _Index = 0
@usableFromInline var _capacity: _Capacity = 6144

init() {
self.ptr = UnsafeMutableRawBufferPointer.allocate(byteCount: Int(_capacity), alignment: 0)
}

@inline(__always) func write(_ ptr: UnsafeRawBufferPointer) {
let bytesCount = ptr.count
let target = UnsafeMutableRawBufferPointer(rebasing: self.ptr.dropFirst(Int(_index)))
target.copyBytes(from: ptr)
self._index += _Index(bytesCount)
}

@inline(__always) func write(byte: UInt8) {
self.ptr[Int(self._index)] = byte
self._index += 1
}

@inline(__always) func toBytes() -> [UInt8] {
return [UInt8](ptr)
}
}

extension WritableBuffer {

func write(json: JSONValue) {

switch json {
case .null:
self.write(byte: UInt8(ascii: "n"))
self.write(byte: UInt8(ascii: "u"))
self.write(byte: UInt8(ascii: "l"))
self.write(byte: UInt8(ascii: "l"))

case .bool(true):
self.write(byte: UInt8(ascii: "t"))
self.write(byte: UInt8(ascii: "r"))
self.write(byte: UInt8(ascii: "u"))
self.write(byte: UInt8(ascii: "e"))

case .bool(false):
self.write(byte: UInt8(ascii: "f"))
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These should be in bulk

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The implementation I use currently looks like this? Do you think this would be faster in this case?

    case .bool(true):
      bytes.append(contentsOf: [
        UInt8(ascii: "t"), UInt8(ascii: "r"), UInt8(ascii: "u"), UInt8(ascii: "e")
      ])

self.write(byte: UInt8(ascii: "a"))
self.write(byte: UInt8(ascii: "l"))
self.write(byte: UInt8(ascii: "s"))
self.write(byte: UInt8(ascii: "e"))

case .string(let string):
self.write(byte: UInt8(ascii: "\""))
string.utf8.withContiguousStorageIfAvailable {
self.write(UnsafeRawBufferPointer($0))
}
self.write(byte: UInt8(ascii: "\""))
case .number(let string):
string.utf8.withContiguousStorageIfAvailable {
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What if contiguous storage isn't available?

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This was just a proof of concept, if I can make it faster with a pointer. So far I can't which is why I don't support nsstring for now. ;)

self.write(UnsafeRawBufferPointer($0))
}
case .array(let array):
var iterator = array.makeIterator()
self.write(byte: UInt8(ascii: "["))
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Iterators copy values more often than needed

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Am I correct in assuming that you would vote for direct array access? for elem in array?

// we don't like branching, this is why we have this extra
if let first = iterator.next() {
self.write(json: first)
}
while let item = iterator.next() {
self.write(byte: UInt8(ascii: ","))
self.write(json: item)
}
self.write(byte: UInt8(ascii: "]"))
case .object(let dict):
var iterator = dict.makeIterator()
self.write(byte: UInt8(ascii: "{"))
if let (key, value) = iterator.next() {
self.write(byte: UInt8(ascii: "\""))
key.utf8.withContiguousStorageIfAvailable {
self.write(UnsafeRawBufferPointer($0))
}
self.write(byte: UInt8(ascii: "\""))
self.write(byte: UInt8(ascii: ":"))
self.write(json: value)
}
while let (key, value) = iterator.next() {
self.write(byte: UInt8(ascii: ","))
self.write(byte: UInt8(ascii: "\""))
key.utf8.withContiguousStorageIfAvailable {
self.write(UnsafeRawBufferPointer($0))
}
self.write(byte: UInt8(ascii: "\""))
self.write(byte: UInt8(ascii: ":"))
self.write(json: value)
}
self.write(byte: UInt8(ascii: "}"))
}
}
}

extension JSONValue {

@available(*, deprecated, message: "Don't use this, this is slow")
public func toBytes() -> [UInt8] {
let buffer = WritableBuffer()
buffer.write(json: self)
return buffer.toBytes()
}
}